The crew, most of whom were divers, were taken by surprise when the 10m-long hardboat Storm Petrel suddenly took on a lot of water in a choppy sea as it approached Lowestoft Harbour at around midday yesterday.
When just a few hundred metres from the harbour entrance, one diver told local television, a “few big waves swamped us at the back”.
The boat was “getting a bit heavy” before it “just tipped and over we went”.
The divers were in undersuits only and no-one had time to don a lifejacket or put out an emergency radio call before struggling to get off the boat.
One group sitting near the stern were taken under before managing to free themselves and surface.
Three people were trapped in the wheelhouse and had to dive under water to get out through an open window in the wheelhouse side.
Had the incident occurred further offshore, with no-one to witness the accident nor any mayday call to alert the Coastguard, the crew would have been in dire straits.
As it was, they were fortunate to be so close to shore and, further, to have the Lowestoft Lifeboat, which happened to be out on exercises, close by.
The lifeboat crew saw the dive boat take an odd attitude, realised it was going and were alongside moments later as the bow section pointed skyward, supported by an air pocket.
The forward part of the wheelhouse was also above water and the lifeboat crew could see the occupants through its sealed windows before they duck-dived to safety.
The crew were picked out of the sea and, after being landed, four were taken to hospital for treatment for ingestion of diesel fuel and shock.
The others were warmed up at the harbour but did not require any other treatment.
The boat settled further but remained partially afloat, just a small portion of the bow protruding from the sea as it drifted until being taken in tow by a recovery vessel.
By yesterday evening it was on the hard at Lowestoft Harbour.
An investigation is to be carried out by the Maritime and Coastguard Agency’s Marine Accident Investigation Branch.
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